Medicament delivery devices such as injectors are sometimes provided with functions where a specific dose can be set by the user, which dose may be varied within a range.
Quite often this dose setting function is performed by turning a knob or wheel at the distal end of the device whereby it is moved in the distal direction. When performing a subsequent injection, the knob is pushed linearly in the proximal direction. One such injector is disclosed in the document U.S. Pat. No. 6,221,053 in which the distal dose knob of the injector is threaded out of a rod barrel tube as a dose is set. Thus the distance the knob is moved in the distal direction is directly related to the dose quantity to be delivered.
One drawback with that type of solution is that if larger doses are to be delivered the dose knob has to be moved quite a long distance in the distal direction, which means that it might be difficult for a user to push the dose knob in the proximal direction during injection. Another drawback of a number of available pen-type drug delivery devices is that they are not reusable in the sense that once the cartridge or vial of medicament is used or exhausted there is no way to remove the old cartridge to replace it with a new cartridge. In other words, once the cartridge is emptied the pen-type device must be thrown away and a new device obtained in order to continue with further administration of the medicament.